The wailing ambulance siren wafts up from the streets of downtown, 500 feet below the roof of the Four Seasons Hotel Denver.

“Here comes our ride,” says a cackling Miles Daisher, a veteran BASE jumping member of the Red Bull Air Force, as he climbs onto the ledge to study the limp wind socks in the vacant hotel parking lot below. Way, way below.

The wisecrack diffuses the intensity as Daisher and fellow Red Bull Air Force BASE jumping athlete Jeff Provenzano prepare to leap from the roof. The original plan was to land in or around the pool below, where hundreds of fancier partyers are sipping cocktails.

The Four Seasons pool is about the size of a dime from this height.

“The pool was the dream,” says Provenzano, admitting to some butterflies. “Glad we pulled that off the table.”

A test jump earlier in the afternoon revealed a pool landing as too sketchy, with the pair gaining too much speed to accurately maneuver their canopies in the heat and altitude.

“Man, elevation is a huge game-changer over here,” says 36-year-old Provenzano, who lives in Arizona.

The pair josh each other, high-fiving several times on the roof.

“This is going to be so fun,” Provenzano says.

“We are going to stick the snot out of this,” Daisher says, pretty much screaming.

Typically their jumps — they share thousands between them and don’t bother to count ( “I’m either jumping or not jumping,” says Provenzano) — are out in the wilds, leaping from bridges or mountaintops. BASE jumping is leaping from fixed objects before releasing increasingly smaller canopies — don’t call them parachutes — to control the descent.

“It’s a party in the landing zone,” says Daisher, after posing for photographs with dozens of spectators eager to share a moment with the 44-year-old who just back-flipped off a 45-story building. “Urban BASE jumping, you gotta love it.”

Jumping in the city is different than the remote cliffs and bridges to which the two flying athletes are accustomed.

“This is a little more dangerous. You got poles, you got buildings, you got traffic, people everywhere,” says Daisher, who jumped wearing a shirt with the face of his friend and Red Bull colleague Shane McConkey, the beloved BASE-jumping freeskier who died in a ski BASE jump in Italy’s Dolomites in 2009 at age 39.

Last week, an international leader in the tightknit world of BASE jumping, Mario Richards, died while wingsuit-flying in Italy’s Dolomites. He was 47.

“This is a BASE jump. It’s not a safe activity. BASE jumping has inherent risks, but we try to do everything safe and smooth and we pretty much nailed it right there,” Daisher says, joining Provenzano in another celebratory high-five. “I’m fired up. What a great view from the top. The skyline is just amazing here.”

The Cradick family was among dozens who gathered to watch the pair’s brief flights. Four-year-old Kelli Cradick posed with her older sister for a photo with Provenzano and Daisher.

“I would never do that,” she says, pointing to the roof. “It’s that high.”

Jason Blevins covers tourism, mountain business, skiing and outdoor adventure sports for both the business and sports sections at The Denver Post, which he joined in 1997. He skis, pedals, paddles and occasionally boogies in the hills and is just as inspired by the lively entrepreneurial spirit that permeates Colorado's high country communities as he is by the views.